Humidifier

ABSTRACT

A humidifier is described for use in combination with a hot air furnace. The humidifier comprises a reservoir which is automatically filled with water from a pressurized water line or supply. Water flows from the reservoir into a boiler and a relatively shallow depth of water is maintained therein. A burner beneath the vaporizer pan comprises a pilot flame which preheats the water, and burner elements which, on demand of a humidistat signal, are fired to generate steam in the boiler. This steam is then introduced into the cold air plenum of the furnace and circulated through the duct system thereof by the furnace blower which is also actuated when there is a demand for increased humidity.

11 1 3,824,985 1451 July 23,1974

1 1 HUMIDIFIER [7 6] Inventor: Sidney W. Hetherington, 5540 Madison Rd., Cincinnati, Ohio 45227 22 Filed: May 1, 1972 21 Appl. No.2 248,981

[52] US. Cl 126/113, 261/141, 261/DIG. 15

[51] Int. Cl F24f 3/14 [58] Field of Search 261/141, DIG. 15; 126/113; 237/78; 236/44 R 3,212,492 10/1965 Himmerich et al. 126/113 3,664,324 5/1972 Radtke 126/113 Primary Examiner-William E. Wayner Assistant Examiner-W. E. Tapolcai, Jr. Attorney, Agent, or Firm-J. Warren Kinney, Jr.

[ ABSTRACT A humidifier is described for use in combination with a hot air furnace. The humidifier comprises a reservoir which is automatically filled with water from a pressurized water line or supply. Water flows from the reservoir into a boiler and a relatively shallow depth of [56] References Cited water is maintained therein. A burner beneath the va- UNITED STATES PATENTS porizer pan comprises a pilot flame which preheats the 1 865 563 7/1932 Greenwald 126/113 water and burner elements which on demand a 1:925:601 9/1933 Pfening 126/113 midistat Signal, are fired generate Steam in the 2,238,108 4/1941 Gates 236/44 R boiler- This Steam is then introduced into the cold air 2,315,070 3/1943 McNaughton 126/113 X plenum of the furnace and circulated through the duct 2,804,870 9/1957 'Chelini 126/113 system thereof by the furnace blower which is 1 a 2,883,006 5/ 59 Martin 236/44 R tuated when there is a demand for increased humidity. 2,993,107 7/1961 Fitchner.... 26l/DIG. 15 3,105,860 10/1963 Dunn 126/113 X 15 Claims, 9 Drawing Figures I I l 1 74 "nhh 6! 5 Q E 70 3 1 i /4 I 62o" Pmmwmzw 3.824.985

SHEET 3 or 3 HUMIDISTAT [26 I20) #4 1 RELAY @L /24{. Q5

RRRR R R CONTROL I22 R 2 e9 FURNACE J m TRANSFORMER COMBINATION BURNER AND SAFETY PILOT CONTROL 76) R RRRRRR i FIG 8 R AND LOW WATER R4 CIRCUIT BREAKER M 1 HUMIDIFIER BACKGROUND OF THE INVENTION The present invention relates to improvements in humidifiers and more particularly to improvements in humidifiers employed in connection with heated living quarters, and also to furnaces incorporating same.

The problems and dangers of dry air in heated buildings or living quarters is well known. Basically, when air is heated to make a building or home comfortable in cold weather, the air is dried out and the artificial atmosphere thus created has an adverse effect on anyone living or working in such atmosphere. For example, the membranes of the nose and throat can be dried out, causing irritation and discomfort. Excessive evaporation of body moisture requires an even greater temperature level for comfort, thus compounding the problems involved. Pets and plants can also be affected in the same fashion by the extremely dry atmosphere created. Further, inanimate objects such as furniture and other wooden components of a'house or dwelling, will shrink and crack, and joints will loosen causing damage of a type well known. Another problem involved in an extremely dry atmosphere is the creation of static electricity. This is not only an annoyance but can be dangerous as well. i

DESCRIPTION OF THE PRIOR ART As indicated above, these problems have long been recognized and thus many humidifiers have beenproposed and several have been put into commercial practice. One of the earlier forms of such devices was simply a container of water mounted on the side of the firebox of a hot air furnace. This container could be filled either manually or automatically, and the water evaporating therefrom would be circulated through the ductwork of the hot air heating system. More recently, the majority, if not all of the commercial devices for providing humidity, or added humidity, to a heated atmosphere, have been so-called cold water systems. A

leading example'of which comprises a rotating screen or drum, partially immersed in a pan of water to provide additional evaporating surface area for transferring water vapor into a circulation system which may be independent of, or used in conjunction with, a hot air heating system. Generally speaking, these cold water systems are relatively inefficient and while they do increase the humidity of the area involved, they are relatively inefficient and introduce certain complications in maintaining a comfort level in conjunction with the heating system itself. A further problem which is most notable in hospitals and other institutions for the treatment of patients suffering from various illnesses, is the fact that such cold water systems can and do become a breeding place for fungus, bacteria, and other micro-organisms, which are then distributed in the circulation of water vapor to increase the humidity level. While hospital patients would be most readily affected by an increase in such micro-organisms in the air in which they breath, it is not unheard of for the level of such micro-organisms to reach a point where it affects healthy persons in homes or working areas.

SUMMARY OF THE INVENTION Accordingly, the broad object of the present invention is to provide an improved humidifying means for increasing the water vapor level in heated areas, or other areas requiring increased humidity.

Another object is to provide an improved humidifier particularly adapted for use in conjunction with forced air heating systems, as well as a heating system incorporating same.

Another object of the invention is to provide an improved humidifier which overcomes the disadvantages of cold water humidifying systems, and particularly eliminates, or essentially eliminates, the possibility of dispersing micro-organisms, or the like, through the areas being humidified.

Another object of the invention is to provide an efficient, effective and inexpensive humidifier having a minimum of moving parts and a minimum cost of installation.

A further object of the invention is to provide an improved humidifier satisfying the above ends and further requiring little or no maintenance.

These ends are broadly attained by a humidifier which comprises a reservoir for water, a boiler into which water is introduced from the reservoir, and a means for heating the water in the boiler to generate steam therefrom. This steam is then dispersed into a living area, or the like, to provide increased humidity when desired.

The humidifier may be utilized independently or adapted for use with a forced hot air furnace or physically incorporated therein. Such furnaces comprise a cold air plenum through which air is drawn by a blower and passed around a firebox and then discharged to a hot air plenum and through ductwork extending to the area to be heated. The steam from the boiler would then be discharged into the cold air plenum for circulation by the blower through the existing ductwork of the furnace and heating system.

Other advantageous features of the invention include means for limiting the level of water in the boiler to a relatively shallow depth and also, the provision of a pilot flame which preheats the water, all of which enables steam to be quickly generated when there is the demand for additional humidity. The demand for additional humidity can be generated by a signal from a humidistat of a type well known in the commercial market. Further, the depth of the reservoir is maintained greater than that of the boiler so that little or no sediment, or the like, will flow into the boiler and impair the steam generating function or otherwise create further maintenance problems. The collection of impurities in the reservoir itself can be further reduced by the introduction of a filter in the main water supply line to the reservoir.

The supply of water to the reservoir is preferably provided by connection of a valve to a pressurized water supply. This valve is controlled by a float mechanism to maintain the water level in the reservoir at a desired depth so that it may then flow through a barrier, or aperture, into the boiler. Further, the float itself has a predetermined minimum position, as indicated by the level of the water in the reservoir, which, when reached, prevents further operation of the steam generating means. This is a safety feature which prevents damage to the boiler or other adjacent components when there is an insufficient supply of water for the generation of steam and the provision of added humidity.

The above and other related objects and features of the invention will be apparent from a reading of the following description of the disclosure found in the accompanying drawings and the novelty thereof pointed out in the appended claims.

DESCRIPTION OF DRAWINGS FIG. 1 is a fragmentary perspective view of a hot air furnace on which a humidifier embodying the present v invention, has been mounted;

FIG. 2 is an enlarged perspective view of the humidifier with portions thereof broken away;

FIG. 3 is a section taken generally on line 3-3 in FIG FIG. 4 isa section taken on line 44 in FIG. 6; FIG. 5 is a section also taken generally on line 33 in FIG. 2, but showing a pilot burner in greater detail;

FIG. 6 is a section taken generally on line 66 in FIG. 2;

FIG. 7 is a view taken generally on line 7-7 in FIG.

Q FIG. 8 is a schematic view of an electrical control system for the humidifier; and

FIG. 9 illustrates a filter which may be employed with the present invention.

DESCRIPTION OF A PREFERRED EMBODIMENT for the air circulated by the blower 17. The products of combustion from the fire box 12 are discharged into the atmosphere through a flue pipe 18. Insofar as the operation of the furnace is concerned, it may be in accordance with any of several known conventional types, usually wherein combustion of fuel and actuation of the blower is initiated by a thermostat.

The humidifier of the present invention (see also FIG. 2) is indicated generally by reference character 24 .and is supplied with water and fuel, preferably gas,

from connections to appropriate sources of supply. The humidifier comprises three basic elements, namely a water reservoir 26, a boiler 28, and a burner 30.

Briefly, the water reservoir 26 is connected to a pressurized source of water through a pipe or tube 29. Water flows from the reservoir into the boiler 28.

- When a remotely located humidistat actuates the burner unit, it is fired and the water in the boiler is heated to generate live steam. This steam is then fed as live steam through a tube 32 into the cold air plenum of the furnace to humidify the air therein and the humidified air distributed through the heating system by the blower 17 which is actuated at the same time as the gas burner is fired.

The gas supply for the burner 30 includes a pipe 36 which is connected to an appropriate supply source, through a shut-off valve 38, which facilitates installation and repair of the burner unit. Gas flow is normally controlled by a conventional burner and safety pilot control 40 which may be selected from several well known controls in the gas fired burner field. Primary flow through such controls is regulated by a solenoid valve with bypass flow to a pilot burner.

Primary flow (see also FIGS. 2 and 7) from the control 40 is through a pipe 42 which is connected to two burner elements 44 disposed beneath the boiler 28. A small line 46 (FIGS. 2, 5, and 7) extends from the control 40 to a pilot burner 48 which heats a thermocouple 50 positioned thereabove, in the conventional fashion of gas burners. The thermocouple is connected by line 52 to the control 40 to provide a signalfor shutting off the flow of gas in the event the pilot light is not lit. When the control 40 is actuated, by a remotely located humidistat, to fire the burner 30, gas flows through the control 40 to the tubes or burner elements 44 and the gas is then ignited by being directed along a cross channel 54 to the pilot 48.

The supply of water to the reservoir 26 is controlled by a valve 56, FIG. 6, which comprises a headed stem 58 which is slidable in' a housing 60 secured to one side of the reservoir 26. The head of the stem 58 is engageable with a seat 61. The housing 60, while provided with means for guiding the stem 58 for axial movement, also provides clearance for flow of water therepast. The housing is connected to the water supply tube 30 and regulation of the valve 56'is controlled by a float 62 which is secured to the outer end of an arm 63. The inner end of this arm is pivotly mounted at 64 on a bracket 66, secured to the side of the reservoir 26. The float 62 rises and falls with the level of the water in the reservoir 26, swinging a lug or block 68 toward and away from the end of the valve stem 58. When the float 62 is at its desired upper level of FIG. 6, the pressure against the stem engages its head with the valve seat 61 to shut off the flow of water. When the float goes below this level,the'lug 68 swings away from the pin 58 and water enters the reservoir, to at all times maintain more or less the desired water level therein. This water then flows through an opening in the form of a tube 70 into the boiler 28. The arm 63 is compositely formed and pivotally clamped at to regulate the level of water in the reservoir 26.

The bottom of the reservoir 26 is a substantial distance below the bottom of the boiler 28, FIG. 4. Water enters the reservoir 26 at a relatively slow rate, thus permitting most, if not all sediment and other solid contaminates, normally found in domestic water supplies, to accumulate on the bottom of the reservoir 26 without being drawn into the boiler 28. Solid contaminates may also be further minimized by a filter 72 (FIGS. 2 and 9) incorporated in the water line 30. The water in the reservoir 26 and boiler 28 is further protected against contamination by loosely fitting covers 74 and 76 respectively which minimize the opportunity for airborne dust, and the like, entering the reservoirand boiler and settling into the water supply system.

The features leading to the control of contaminants are of great significance in minimizing the maintenance required for the present humidifier as well as minimizing, if not essentially eliminating dispersion of such contaminants by the blower which disperses the water vapor. Thus any sediment or the like which does enter the reservoir 26 will settle to the bottom and require periodic cleaning only at very extended intervals. The boiler itself should be essentially free of such contaminants which is an important factor in preserving the effectiveness of its steam generating capabilities, as well '5 as in eliminating entrainment of contaminates in the steam vapor circulated forhumidification.

It will further be noted that there is no waste water drain since the depth of water in the boiler, as provided by the present water supply system, is maintained at a relatively shallow level. This feature, particularly in combination with the preferred use of the pilot burner 48 enables an extremely fast response time when there is a demand for increased humidity. The pilot burner 48 maintains the water economically, at an elevated temperature below its boiling point. Thus when the burner elements 44 are fired, steam is quickly generated. The steam generating-process also kills all normal fungus or other microorganisms which might be harmful if circulated to living areas.

Another feature of the invention is found in means for preventing operation of the burner 30 when there is an insufficient water supply. These means comprise a switch 78, FIG. 6, which is mounted on a bracket 80 projecting from one side of the reservoir 26 above the float arm 63. The switch 78 includes a pair of contacts 82, 84. Electrical leads86, 88 are connected to the contact 84 and electrical lead 90 is connected tothe contact 82. A conductive plate 92 is pivotally mounted on the contact 82 and a spring 94 normally maintains the switchplate in engagement with the other contact 84. An insulated screw 96 depends from the plate 92. A link 98 embraces the head of the screw 96 and has a bent portion 100 underlying the arm 63. In normal operation, with an adequate water supply, movement of the float arm 63 is insufficient to open the switch 78. However, when the level of the water in the reservoir 26 is insufficient to supply water to the boiler 28, the float 62 falls to a level sufficient to cause the link 98 to displace the switchplate 92 and open the switch 78. When this occurs, and as will later be explained in further detail, the control-40 is rendered inoperative and gas will no longer be fed therethrough. This prevents the boiler from being heated in a dry condition where excessive heat could either damage the pan itself or cause damage to adjacent components of the humidifier, or possibly the furnace.

It will also be noted that the humidifier 24 may take the form of a self-contained unit for attachment to an existing furnace. This is best illustrated in FIG. 2 which shows brackets 102 to which the boiler and burner unit are secured. The reservoir 24 may, in turn, be welded or brazed to the boiler. This self-contained unit then may be readily mounted on an existing furnace simply by the use of screws which would pass through the illustrated holes in the bracket 102 in securing it to the plenum or plenums of the furnace.

Another feature to be noted is the provision of a collector hood 104 which overlies the reservoir 26 and boiler 28. The collector hood 104 has a depending skirt which extends to or somewhat below the level of the burner tubes 44. In this fashion the products of com bustion of the burner 30 are collected in the hood 104 and then vented through a conduit 106 to the flue pipe 18 of the furnace for ultimate discharge to the atmosphere.

Next referencing FIG. 8, the electrical circuit of the I present invention will be described. The electrical circuit is particularly adapted for incorporation into a typical electrical control circuit for a forced air heating system. The circuit itself may be energized by connections to the low voltage output of a furnace transformer indicated at 108. For convenience of installation a junction block 110 may be employed and mounted on one of the plenums of the furnace as indicated in FIG. 1. One side of the transformer 108 is connected by lead 112 to the junction block 110, utilizing the same reference character line 112, connection is then made to a humidistat 114. The humidistat 114, which has previously been referenced herein is, in effect, a switch which operates in essentially the same fashion as a thermostat only it is responsive to humidity levels rather than temperature. The opposite side of the humidistat 114 is connected by lead 116 to the junction block 110 and then through lead to the switch 78, which is herein given the legend combination float valve and low water circuit breaker. Leads 86 and 88 extend respectively from the switch 78 to the junction block and one side of the burner and safety pilot control 40. The opposite side of the control 40 is connected by a lead 118 to the junction block 110 and then to the opposite side of the furnace transformer 108. The lead 86 extends, through the junction block 110, to a relay 120, the opposite side of which is connected by line 122 through the junction block 110 back to the opposite side of the furnace transformer 108. When the relay is energized, a circuit is completed through lines 124 to a furnace blower control 126 to actuate the blower 17, previously referenced in connection with FIG. 1.

It will be apparent from the preceeding that the humidistat 114 is the primary control for the humidifier circuit. When this switch is closed the control 40 is actuated to fire the burner 30 and at the same time the relay 120 is energized to actuate the furnace blower 17. In case the switch 78 is open due to an insufficient water supply, neither the control 40 nor the blower 17 can be actuated since the switch 78 is in series with the humidistat switch. Further, theconnections with the furnace blower control 126 are in parallel with other controls therefor so that there is no interference with normal operation of the furnace. Thus, the humidifier can operate independently of the furnace, or it can operate at the same time as the furnace is operating. In any event, the two electrical circuits are independent in so far as any functional interrelationship is concerned; I

While there are certain advantages to the use of gas as the fuel for generating steam in the boiler 28, other fuels or electricity could also be employed. Also, it will be apparent that the hood 104 could be constructed to serve the dual function of providing covers for the reservoir 26 and boiler 28. Also, the humidifier could be employed independently of a hot air furnace, could be manufactured as a unit for attachment to an existing hot air furnace as described, or could be built directly into such a furnace as an integral part thereof. Another variation to be noted is that the supply of waterto the boiler could be over the top of a barrier or through a notch in such barrier, instead of through the illustrated passageway in a barrier wall. These and other variations of the described preferred embodiment will be apparent to those skilled in the art, and the spirit and scope of the inventive concepts herein should therefore be judged solely from the following claims.

What is claimed is:

1. A self-contained, compact steam humidifier for introducing steam into a space to increase the relative humidity thereof and at the same time reduce the possibility of dispersing harmful micro-organisms into the space being humidified, comprising a closed reservoir having opposite side and end walls and a bottom wall, water inlet means in one of said walls for flow of water into said reservoir, float controlled valve means in said inlet means to control flow of "water through said inlet means in response to the level of water in said reservoir, closed boiler means adjacent said reservoir and having opposite side and end walls, a top wall and a bottom wall, water passage means extending from the reservoir to adjacent the bottom of the boiler for flow of water from the reservoir to the boiler, burner means 7 adjacent the bottom wall of the boiler to heat and boil water in the boiler to thus generate steam from the water in said boiler, humidistat means operatively connected-with said burner means to control operation of said burner means in response to the relative humidity 7. humidifier as in claim 6, including means con 7 nected in series with the humidistat and switch and with in said space tobe humidified, steam outlet means extending from an upper portion of said boiler and opera tively associated with a forced air furnace system for dispersing steam from said boiler to said space to humidified, said steam increasing the humidity of the air in said space without lowering the temperature thereof and at the same time reducing the possibility of dispersing harmful micro-organisms into said space, hood means disposed over said boiler and said reservoir and having a skirt portion extending to approximately the level of said burner means to confine the products of combustion of said burner means, and aconduit means extending from an upper portion of said hood means for venting the products of combustion of said burner means.

2. A humidifier as in claim 1, wherein said water passage means is spaced a relatively short distance above the bottom wall of the boiler and wherein the bottom wall of the reservoir at least at the point of said water passage, is spaced a substantial distance below the bottom wall of the boiler, and means connected with said water supply means for limiting the height of the water in said reservoir to an upper level somewhat above the bottom wall of said boiler to thus maintain a relatively shallow depth of water in the boiler.

3. A humidifier as in claim 2, wherein the means for limiting the height of water in the reservoir comprises a float controlled valve in said water supply means for said reservoir.

4. A humidifier as in claim 3, including means responsive to said float for preventing operation of said heater means when the level of water in said reservoir is below a predetermined level.

5. A humidifier as in claim 4, wherein said heater means comprises a gas-fired primary burner and a pilot burner, control means connected with said primary burner and pilot burner for controlling the supply of gas to said burners, said pilot burner being normally supplied with gas and ignited to maintain the water in the boiler at an elevated temperature below the boiling temperature thereof and the control means being responsive to a humidistat to supply gas to the primary burner, which gas will be ignited from the pilot burner to provide additional heat to quickly generate steam in said boiler when demanded by said humidistat.

6. A humidifier as in claim 5,-including a switch means connected in series between said humidistat and said control means for said primary burner and pilot burner, said switch means being normally closed and opened in response to movement of said float when the means for actuating a blower of a furnace so that the furnace blower will automatically be actuated by the humidistat when there is a demand for increased humidity, and will not operate when there is a low level of water in the boiler.

8. A humidifier as in claim 3, wherein said float controlled valve comprises a float attached to a pivotally mounted arm, a valve housing connected to one end thereof to the source of water for receiving water therefrom, a valve stem axially slidable in said housing and having a head thereon engageable with a seat formed in said housing to shut off flow of water through said valve, said housing having a clearance space around said stern and head for passage of water therearound into said reservoir when said valve is open, and a lug secured to said that arm in a position for engagement with said stem to move said stem to close said valve when the water'in said reservoir reaches said upper level.

9. A humidifier as in claim 1, wherein the space into which the steam is introduced is the cold air plenum of a hot air furnace which also includes a hot air plenum, a fire box, and a blower for drawing air into the cold air plenum andcirculating it over saidfire box and discharging itintothe hot air plenum for circulation to areas to be heated, said steam outlet means of said boiler connected with said cold air plenum for discharging steam generated in said boiler into the plenum for circulation by said blower. 10. A humidifier as in claim 1, wherein a cover is disposed on each of said boiler and said reservoir to minimize introduction of airborne contaminants therein, and a filter is positioned in the water supply means to minimize, if not eliminate, contaminants entering said reservoir.

11. A humidifier as in claim 1, wherein said-burner means comprises a gas-fired burner disposed beneath said boiler, and means connectedwith said gas-fired burner and a source of pressurized gas. I

12. A humidifier as in claim 11, wherein the gas-fired burner includes two heating elements, one of said heating elements being continuously energized to maintain the water in the boiler at an elevated temperature below the boiling point thereof, and the other of said heating elements being energized responsive to said humidistat to provide additional heat sufficient to generate steam from the water in said boiler.

13. A humidifier as in claim 12, wherein one of said heating elements comprises a gas-fired primary burner, and the other of said heating elements comprises a pilot burner, control means connected with said primary burner and pilot burner for controlling the supply of gas thereto to normally supply said pilot burner with gas to maintain the water in the boiler at said elevated temperature, and said control means being responsive to said humidistat to supply gas to the primary burner which gas is ignited from the pilot burner to provide additional heat to quickly generate steam in said boiler, when demanded by said humidistat.

14. A humidistat as in claim 1, wherein said reservoir is supported on said boiler, and said burner means is supported on said boiler, bracket means secured to the boiler to support the boiler, reservoir and burner means as a unit to a support surface adjacent the space being humidified.

15. A self-contained, compact steam humidifier for introducing steam into a space to increase the relative humidity thereof and at the same time reduce the possibility of dispersing harmful micro-organisms into the space being humidified, comprising a closed reservoir having opposite side and end walls and a bottom wall,

' water inlet means in one of said walls for flow of water into said reservoir, float controlled valve means in said inlet means to control flow of water through said inlet means in response to the level of water in said reservoir, closed boiler means adjacent said reservoir and having opposite side and end walls and a bottom wall, water passage means extending from the reservoir to adjacent the bottom of the boiler means for flow of water from the reservoir to the boiler, heater means adjacent the bottom wall of the boiler to heat and boil water in the boiler to thus generate steam from the water in the boiler, a humidistat means operatively connected with said heater means to control operation of said heater means in response to the relative humidity in said space, normally closed switch means connected in series with said humidistat and said heater means and operative in response to a predetermined low level of water in said reservoir and said boiler to open to prevent operation of said heater means, steam outlet means extending from an upper portion of said boiler to a cold air plenum chamber of a furnace to disperse said steam into said plenum chamber to be dispersed by said furnace into the space to be humidified, and means connecting the humidistat means and switch means in series with a blower of said furnace for operating the blower means of the furnace when there is a demand for increased humidity and to prevent operation of said blower means when the level of water in the reservoir is below a predetermined amount. 

1. A self-contained, compact steam humidifier for introducing steam into a space to increase the relative humidity thereof and at the same time reduce the possibility of dispersing harmful micro-organisms into the space being humidified, comprising a closed reservoir having opposite side and end walls and a bottom wall, water inlet means in one of said walls for flow of water into said reservoir, float controlled valve means in said inlet means to control flow of water through said inlet means in response to the level of water in said reservoir, closed boiler means adjacent said reservoir and having opposite side and end walls, a top wall and a bottom wall, water passage means extending from the reservoir to adjacent the bottom of the boiler for flow of water from the reservoir to the boiler, burner means adjacent the bottom wall of the boiler to heat and boil water in the boiler to thus generate steam from the water in said boiler, humidistat means operatively connected with said burner means to control operation of said burner means in response to the relative humidity in said space to be humidified, steam outlet means extending from an upper portion of said boiler and operatively associated with a forced air furnace system for dispersing steam from said boiler to said space to humidified, said steam increasing the humidity of the air in said space without lowering the temperature thereof and at the same time reducing the possibility of dispersing harmful micro-organisms into said space, hood means disposed over said boiler and said reservoir and having a skirt portion extending to approximately the level of said burner means to confine the products of combustion of said burner means, and a conduit means extending from an upper portion of said hood means for venting the products of combustion of said burner means.
 2. A humidifier as in claim 1, wherein said water passage means is spaced a relatively short distance above the bottom wall of the boiler and wherein the bottom wall of the reservoir at least at the point of said water passage, is spaced a substantial distance below the bottom wall of the boiler, and means connected with said water supply means for limiting the height of the water in said reservoir to an upper level somewhat above the bottom wall of said boiler to thus maintain a relatively shallow depth of water in the boiler.
 3. A humidifier aS in claim 2, wherein the means for limiting the height of water in the reservoir comprises a float controlled valve in said water supply means for said reservoir.
 4. A humidifier as in claim 3, including means responsive to said float for preventing operation of said heater means when the level of water in said reservoir is below a predetermined level.
 5. A humidifier as in claim 4, wherein said heater means comprises a gas-fired primary burner and a pilot burner, control means connected with said primary burner and pilot burner for controlling the supply of gas to said burners, said pilot burner being normally supplied with gas and ignited to maintain the water in the boiler at an elevated temperature below the boiling temperature thereof and the control means being responsive to a humidistat to supply gas to the primary burner, which gas will be ignited from the pilot burner to provide additional heat to quickly generate steam in said boiler when demanded by said humidistat.
 6. A humidifier as in claim 5, including a switch means connected in series between said humidistat and said control means for said primary burner and pilot burner, said switch means being normally closed and opened in response to movement of said float when the water in said reservoir falls to a level below the lower level of a passageway connecting the reservoir outlet and boiler inlet, thereby preventing operation of the burners when water is not being supplied to the boiler.
 7. A humidifier as in claim 6, including means connected in series with the humidistat and switch and with means for actuating a blower of a furnace so that the furnace blower will automatically be actuated by the humidistat when there is a demand for increased humidity, and will not operate when there is a low level of water in the boiler.
 8. A humidifier as in claim 3, wherein said float controlled valve comprises a float attached to a pivotally mounted arm, a valve housing connected to one end thereof to the source of water for receiving water therefrom, a valve stem axially slidable in said housing and having a head thereon engageable with a seat formed in said housing to shut off flow of water through said valve, said housing having a clearance space around said stem and head for passage of water therearound into said reservoir when said valve is open, and a lug secured to said float arm in a position for engagement with said stem to move said stem to close said valve when the water in said reservoir reaches said upper level.
 9. A humidifier as in claim 1, wherein the space into which the steam is introduced is the cold air plenum of a hot air furnace which also includes a hot air plenum, a fire box, and a blower for drawing air into the cold air plenum and circulating it over said fire box and discharging it into the hot air plenum for circulation to areas to be heated, said steam outlet means of said boiler connected with said cold air plenum for discharging steam generated in said boiler into the plenum for circulation by said blower.
 10. A humidifier as in claim 1, wherein a cover is disposed on each of said boiler and said reservoir to minimize introduction of airborne contaminants therein, and a filter is positioned in the water supply means to minimize, if not eliminate, contaminants entering said reservoir.
 11. A humidifier as in claim 1, wherein said burner means comprises a gas-fired burner disposed beneath said boiler, and means connected with said gas-fired burner and a source of pressurized gas.
 12. A humidifier as in claim 11, wherein the gas-fired burner includes two heating elements, one of said heating elements being continuously energized to maintain the water in the boiler at an elevated temperature below the boiling point thereof, and the other of said heating elements being energized responsive to said humidistat to provide additional heat sufficient to generate steam from the water in said boiler.
 13. A humidifier as in claim 12, wherein one of said heating elemenTs comprises a gas-fired primary burner, and the other of said heating elements comprises a pilot burner, control means connected with said primary burner and pilot burner for controlling the supply of gas thereto to normally supply said pilot burner with gas to maintain the water in the boiler at said elevated temperature, and said control means being responsive to said humidistat to supply gas to the primary burner which gas is ignited from the pilot burner to provide additional heat to quickly generate steam in said boiler, when demanded by said humidistat.
 14. A humidistat as in claim 1, wherein said reservoir is supported on said boiler, and said burner means is supported on said boiler, bracket means secured to the boiler to support the boiler, reservoir and burner means as a unit to a support surface adjacent the space being humidified.
 15. A self-contained, compact steam humidifier for introducing steam into a space to increase the relative humidity thereof and at the same time reduce the possibility of dispersing harmful micro-organisms into the space being humidified, comprising a closed reservoir having opposite side and end walls and a bottom wall, water inlet means in one of said walls for flow of water into said reservoir, float controlled valve means in said inlet means to control flow of water through said inlet means in response to the level of water in said reservoir, closed boiler means adjacent said reservoir and having opposite side and end walls and a bottom wall, water passage means extending from the reservoir to adjacent the bottom of the boiler means for flow of water from the reservoir to the boiler, heater means adjacent the bottom wall of the boiler to heat and boil water in the boiler to thus generate steam from the water in the boiler, a humidistat means operatively connected with said heater means to control operation of said heater means in response to the relative humidity in said space, normally closed switch means connected in series with said humidistat and said heater means and operative in response to a predetermined low level of water in said reservoir and said boiler to open to prevent operation of said heater means, steam outlet means extending from an upper portion of said boiler to a cold air plenum chamber of a furnace to disperse said steam into said plenum chamber to be dispersed by said furnace into the space to be humidified, and means connecting the humidistat means and switch means in series with a blower of said furnace for operating the blower means of the furnace when there is a demand for increased humidity and to prevent operation of said blower means when the level of water in the reservoir is below a predetermined amount. 